Biology 189 Chapter 2 Homework

electron-sharing Only in covalent bonds do atoms share electrons.

A phrase that applies to covalent bonding and not other kinds of bonds is .. - charge attraction. - great strength. - paired electrons. - electron-sharing. - All of the above.

element

A substance that cannot be broken down into other substances by ordinary chemical procedures is a(n) __ -molecule -element -proton -isotope -compound

double covalent The oxygen atoms are sharing two pairs of electrons.

A(n) _____ bond joins these two oxygen atoms. -single covalent - quadruple covalent - ionic - double covalent - hydrogen

molecule A molecule is defined as two or more atoms held together by covalent bonds.

A(n) _____ refers to two or more atoms held together by covalent bonds. - isotope - molecule - community - ion - shell

the number of unpaired electrons in the valence shell The fullness of the valence shell determines the pattern of covalent bonding or ionization. The reactivity of an atom is a function of the presence of unpaired electrons in one or more orb

The type of bonding and the number of covalent bonds an atom can form with other atoms is determined by - the number of protons - the number of unpaired electrons in the valence shellt - the nucleus - the size of the atom: smaller atoms are chemically more reactive - the number of neutrons

nonpolar covalent bond Atoms with similar electronegativities form nonpolar covalent bonds.

A carbon atom and a hydrogen atom form what type of bond in a molecule?

C; it has 6 protons. Atoms represent the element carbon (C) if they have six protons.

An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because - C; it has 6 protons. - C; it has 6 electrons. - N; it has 6 electrons. - N; it has 6 protons. - O; its mass number is 12.

10 neutrons Isotopes have the same number of protons; different numbers of neutrons.

An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have ... - 9 protons - 7 electrons - mass number 16, atomic number 7. - 10 neutrons. - All of the above

3 The neutral atom has 7 electrons. Two electrons fill the first shell, and 5 go into the second (valence) shell. The atom needs 3 more electrons to fill the valence shell.

An atom's atomic number is 7. Its valence is most likely ... - 1 - 2 - 7 - 3 - 5

1

An electrically neutral molecule has the formula C3H4O2N. If the carbon atoms form the usual number of bonds, how many covalent bonds will each hydrogen atom have with other atoms in the molecule? - 4 - 2 - 3 - 5 - 1

an attraction between ions of opposite charge

An ionic bond involves _____. - the unequal sharing of an electron pair - water avoidance - an attraction between ions of opposite charge - no atoms other than sodium and chlorine - the sharing of a single pair of electrons

one atom transfers an electron to another atom Transfer of an electron from one atom to another results in a positive ion (cation) and a negative ion (anion), which usually attract each other to form an ionic bond. However, the ions need not have acquired their electrical charge due to an electron transfer with each other.

An ionic bond is formed when

are different ions Ions are charged atoms.

Atoms with the same number of protons but with different electrical charges _____. - are different isotopes - have different numbers of neutrons - have different atomic numbers - are different ions -have different atomic masses

Shared electrons aren't always near oxygen. Oxygen keeps 6 electrons to itself. The 4 shared electrons migrate between O and the other atoms, thus contributing 4 half-charges to oxygen. This gives oxygen about 8 units of negative charge, balancing the atom's 8 protons.

By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero? - The valence shell has 6 electrons. - The atom has 8 electrons. - The atom lost electrons from other shells. - Shared electrons aren't always near oxygen. - The charge isn't near zero; it's -2.

protons Elements are defined by the number of protons. Protons give an enduring basis for atomic behavior because they are permanently anchored in the nucleus, where their attraction determines how many electrons the atom can hold. By contrast, electrons come and go, and the numbers vary. Isotopes of the same element vary in the number of neutrons in the nucleus of the atom.

Chemists assign atoms to chemical elements by counting their ________. -electrons -neutrons -isotopes -protons

the third option The farther an electron shell is from the nucleus, the more potential energy an electron has to gain in order to move into it.

Compare the three atom diagrams. Which one shows the electron with the highest potential energy?

do both (a) and (b). (a) fill shells without giving atoms much charge. (b) bring electrons closer to protons. Right! Electron-sharing brings electrons closer to nuclei and it fills shells without giving the atoms much charge. Both factors stabilize the bond.

Covalent bonds hold atoms together because they ... - (a) fill shells without giving atoms much charge. - (b) bring electrons closer to protons. - (c) use forces between nuclei as well as forces between electrons. - do all of the above. - do both (a) and (b).

the first shell shouldn't have 3 electrons. The first shell can only have 0, 1, or 2 electrons.

Dr. Jones says an atom has 3 electrons in the first shell and four electrons in the second shell. Someone should tell Dr. Jones that... - the first shell must fill before the second shell can have electrons. - the second shell can't have 4 electrons. no shell can hold more than 2 electrons. - the first shell shouldn't have 3 electrons. - the second shell should have 8 electrons.

1. When an electron absorbs the required amount of light energy, it moves from a lower electron shell to a higher electron shell, which is farther from the nucleus. 2. When an electron loses a discrete amount of energy, it moves from a higher electron shell to a lower electron shell, which is closer to the nucleus. Movement of electrons between shells requires input or release of discrete amounts of energy.

Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Terms may be used more than once. 1. When an electron absorbs the required amount of light energy, it moves from a ___ electron shell to a ___ electron shell, which is ___ the nucleus. 2. When an electron loses a discrete amount of energy, it moves from a ___ electron shell to a ___ electron shell, which is ___ the nucleus. lower higher farther from closer to

All organisms evolved on Earth (with its unique elemental composition), and all are genetically related to one another. Species living under unusual conditions might differ more than others, though. We also might predict that the more similar the percentages of naturally occurring elements are in two species, the more closely related those two species are.

EVOLUTION CONNECTION The percentages of naturally occurring elements making up the human body are similar to the percentages of these elements found in other organisms. How could you account for this similarity among organisms?

Attraction to the positively charged protons in the nucleus Electrons have a negative charge, and so are attracted to the positive charge of the protons in the nucleus, which holds them in the atom.

Electrons are held in an atom by attraction to what particle or location? - Attraction to the magnetic neutrons in the nucleus - Attraction to the positively charged protons in the nucleus - Attraction to the other electrons in the atom - Attraction to the lowest electron shell

electrons in two orbitals. A double bond involves two orbitals, each with a shared pair of electrons.

In a double covalent bond, a carbon atom shares ... - two electrons. - electrons in two orbitals. - electrons in two of its shells. - both valence and nonvalence electrons. - None of the above.

4, 1, 2, 3

In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively - 4, 1, 2, 3 - 4, 1, 3, 22, - 1, 3, 43, 2, - 4, 23, 2, 1, 4

ionic Sodium and chlorine ions are attracted to each other.

In salt, what is the nature of the bond between sodium and chlorine? - polar covalent - hydrogen - nonpolar covalent - ionic - hydrophobic

Proton: symbol P +1 charge Neutron: symbol N 0 charge Electron symbol e -1 charge The proton, neutron, and electron are the three main subatomic particles that make up all the elements.

Match each property to the appropriate subatomic particle. Drag each property into the correct bin. proton neutron electron symbol e symbol n symbol p +1 charge 0 charge -1 charge

(a) a covalent bond links atoms of two kinds. (b) atoms share electrons unequally. both (a) and (b) Each kind of atom has a different attraction for electrons. Thus, atoms of different kinds share electrons unequally. That gives one atom a partial negative charge; the other atom a partial positive charge.

Partial charges occur when ... - (a) a covalent bond links atoms of two kinds. - (b) atoms share electrons unequally. - (c) two ions are close together. - any of the above occur. - both (a) and (b).

an atom has too many neutrons. The atomic nucleus becomes unstable if the ratio of protons to neutrons is too far from unity.

Radioactive decay is likely to occur when ... - atoms collide with one another. - an atom has too many neutrons. - an electron hits the nucleus. - an atom has too many electrons. - protons break into neutrons and electrons.

helium

Refer to the following figure (first three rows of the periodic table) to answer the questions below. What element does not react with other elements? -helium -oxygen -silicon -hydrogen

mass of ~1 amu: proton neutron mass of ~1/2000 amu electron The proton and neutron both have masses of about 1 amu, whereas the electron mass is only about 5.5×10^-4 amu

Sort the subatomic particles according to their masses. Drag each subatomic particles into the correct bin. mass of ~1 amu mass of ~1/2000 amu proton neutron electron

all of the above Since N has 7 protons, it must fill the second shell, giving it 4 pairs of electrons. The electrons form 3 bonds and 1 lone pair of electrons. Each pair of electrons repels the other pairs, so they are equally far apart.

The ammonia molecule in the diagram has the observed bond orientation because ... - electrons repel one another. - N has 7 protons in its nucleus. - N has four pairs of electrons in the valence shell. - All of the above. - None of the above.

hydrogen A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.

The brackets are indicating a(n) _____ bond. - ionic - hydrogen - single (nonpolar) covalent - polar covalent - hydrophobic

8 neutrons in the nucleus. The atomic number (7) gives the number of protons, and the mass number is the number of protons plus neutrons.

The mass number of an atom is 15, and its atomic number is 7. The atom probably has...

the existence of unpaired electrons in the valence shell.

The reactivity of an atom arises from

4 There are four electrons in the outermost electron shell.

This atom can form up to _____ single covalent bond(s).

2 electrons The neutral atom has 8 electrons. Two electrons fill the first shell, and 6 go into the second (valence) shell. Two more electrons would fill the valence shell.

To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ... - 1 electron. - 8 electrons. - 3 electrons. - 2 electrons.

All the atoms lie in a plane. The double bond limits all the atoms to a plane.

Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true? - The bonds orient in a tetrahedral fashion. - All the atoms lie in a line. - All the atoms lie in a plane. - The groups rotate around the C=C bond. - The bonds orient like tripods or pyramids.

the same number of protons. The number of protons defines a chemical element. The number of neutrons and electrons can differ among atoms of the same element.

Two atoms always represent the same element if they have ... - the same mass number. - the same number of shells. - the same number of particles in the nucleus. - the same number of protons. - the same number of electrons.

- It can move out to a higher electron shell. - It can stay in its original shell. The electron will move out to a higher shell if the sunlight provides the correct, discrete amount of energy. If the sunlight does not provide the correct amount of energy, the electron will remain in its original shell.

What can happen to an electron when sunlight hits it? Select all that apply. - It can collide with the nucleus. - It can move out to a higher electron shell. - It can drop down to a lower electron shell - It can stay in its original shell.

265 106+158+1

What is the mass number of an ion with 106 electrons, 158 neutrons, and a +1 charge?

hydrogen A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.

What name is given to the bond between water molecules? - ionic - single (nonpolar) covalent - polar covalent - hydrophobic - hydrogen

covalent A covalent bond is one in which electron pairs are shared.

What type of bond is joining the two hydrogen atoms? - hydrophilic - hydrogen - ionic - covalent - hydrophobic

single (nonpolar) covalent Each carbon-hydrogen bond involves a single pair of equally shared electrons.

What type of bond joins the carbon atom to each of the hydrogen atoms? -ionic - polar covalent - single (nonpolar) covalent - double (nonpolar) covalent - hydrogen

O, N, C, H Remember this, and you'll be able to predict polarity when molecules have O or N linked to C or H.

Which answer correctly ranks the atoms in terms of decreasing electronegativity (the highest electronegativity first)?

The valence shell needs 8 electrons. Without help, C can only hold 4 electrons in the valence shell. To fill the shell, 4 more electrons must be shared, making 4 covalent bonds.

Which answer helps to explain why carbon atoms tend to make 4 covalent bonds? - The valence shell needs 8 electrons. - The first electron shell has 4 orbitals. - The carbon nucleus has 4 protons. - All of the above. - None of the above; carbon makes 3 covalent bonds.

Probability model We cannot determine the exact motion of electrons. We can only compute the regions where electrons occur most of the time. To emphasize the uncertainty, a diagram showing random motion is more suitable than planetary paths.

Which model most accurately represents the current view of the structure of the atom?

Magnesium By weight, magnesium accounts for only 0.1% of most living things.

Which of the following is a trace element found in the human body? Oxygen Hydrogen Nitrogen Magnesium Carbon

proton Each proton has one unit of positive charge.

Which of the following subatomic particles always has a positive charge? See Concept 2.2 (Page) -electron -neutron -element - proton - atom

the fourth option Oxygen is more electronegative than hydrogen.

Which of these figures correctly illustrates the nature of the bonding of H2O? *pay attention to the charges*

The atom has more electrons than protons.

Which statement is true of all atoms that are anions? - The atom has more electrons than protons. - The atom has more neutrons than protons. - The atom has fewer protons than does a neutral atom of the same element. - The atom has more protons than electrons.

Electrons determine the atom's size. With electrons on the surface, atoms repel one another when they come too close. Thus, electrons determine the space that an atom occupies.

Which statement is true of atoms? - Most of an atom's volume is filled with matter. - Protons attract other protons. - Electrons determine the atom's size. - Protons repel electrons. - All of the above.

All of the above The atom has a vacancy in its inner shell; an electron has moved to the outer (valence) shell. The result is an unstable excited state. An electron will move back to the inner shell, restoring the ground state as the atom gives off energy.

Which statement is true of the atom shown in the diagram? - The atom has more than one valence electron. - An electron will move from the outer to the inner shell. - The atom is in the excited state. - All of the above. - None of the above.

The valence shell has higher energy than other occupied shells. The outer occupied shell is the valence shell, and outer shells hold electrons at higher energy than inner shells.

Which statement is true of the energy levels of electrons in shells? - Electrons must lose energy to move from the first to the second shell. - The valence shell has higher energy than other occupied shells. - All the electrons in an atom have similar amounts of energy. - All of the above. - None of the above.

- rotation can occur around single bonds. Rotation allows groups of atoms to change position while preserving the usual bond angles around each atom.

Without making or breaking bonds, the pictured molecule can change its shape because ... - electrons can move from one bond to another. - rotation can occur around single bonds. - some atoms make longer bonds than others. - proximity of other atoms alters bond angles. - None of the above.